The ability to reproduce endotoxin shock in mice provides a unique opportunity to study the biology of the disease and its consequences. The studies proposed here take advantage of the ease of doing experiments in mice and the newest genetic technology. Dr. Goyert has recently produced mice in which the CD14 gene has been disrupted by homologous recombination. These mice provide a unique opportunity to ask several fundamental questions about the nature of endotoxin shock, particularly as regards CD14- dependent and CD14-independent pathways to endotoxin shock. In addition, this animal model will allow Dr. Goyert to evaluate the relative contribution of endothelial cell responses to sCD14- LPS complexes in endotoxin shock.This is the first time that such a model has been established for delineating the effects of these three mechanisms. She will also continue development of a new animal model that will respond to endotoxin in a CD14-dependent manner through the human CD14 protein. This model will be used to evaluate the efficacy of reagents (anti-human CD14 mAb, recombinant soluble human CD14) on the endotoxin response of mice expressing a human CD14 gene and lacking expression of the murine CD14 gene. The following questions will be addressed: 1. How does the lack of CD14 affect the response of CD14-knockout mice to LPS, Gram-negative bacteria, Gram-positive bacteria, and complexes of LPS and soluble CD14? 2. How effective are soluble human CD14 and anti-human CD14 mAb in preventing endotoxin shock in mice expressing human but not murine CD14? Furthermore, can efficacious, unique CD14-specific mAbs be generated in CD14-deficient mice? 3. What is the three-dimensional structure of CD14? 4. What is the nature of the endothelial cell receptor for the complex of LPS-soluble CD14 and is it present on other cell types that also respond to this complex?